Effect of the selenium supplemented diets on O. mykiss physiological traits. A Representative images of livers with hematoxylin–eosin staining of fish fed with the experimental diets SSD1, SSD5, and SS10, and their respective digital zoom of 10%. Bars = 10 µm. B and C Biochemical measurements of enzymes indicative of liver damage (n = 5). D Plasma selenium concentration of O. mykiss fed with different concentrations of selenium in the diet measured by Total X-ray fluorescence spectroscopy (TXRF) at 60 days post-treatment (dpt) (n = 3). E Hydrophilic antioxidant capacity in plasmas from O. mykiss fed with different selenium concentrations in the diet measured by oxygen radical antioxidant capacity (ORAC) assay at 60 dpt (n = 5). Different letters represent significant differences (ANOVA p < 0.05, post hoc analysis Tukey).